The invention is based on a hydraulic brake system as defined hereinafter. A brake system of this kind is known from International Patent Disclosure WO 91/16221.
In such brake systems, the problem is that the brake system, if its full effectiveness is to be assured, must be vented either before it is filled, or while it is being filled, with hydraulic medium, in other words a fluid such as DOT4. Any air bubbles still present in the hydraulic medium may bring about such an elasticity of fluid columns formed by the medium that the brake pressures required in wheel brake cylinders are not brought about to the requisite level. This is especially true in hydraulic brake systems of the kind that work with a brake booster under high-pressure conditions and/or the kind that are equipped with an anti-lock brake system (ABS) and/or a traction control system (ASR).
Brake systems of this kind have several electromagnet valves that are closed in the state of repose; the valves of return pumps used in these brake systems are normally closed as well.
The problem therefore exists that pockets of air may be present downstream of the magnet valves closed in the position of repose and also downstream of the return pump valves. The air in these pockets may possibly be removed only with difficulty using liquid.
It has also already been proposed that at least the magnet valves closed in the state of repose be triggered electrically upon evacuation prior to filling of the system and thereby opened. To do so, however, special plug connections must be used to supply current to these magnet valves. Special plug connections of this kind are complicated to manufacture and are also expensive and involve operating costs when used.